This invention relates to hydrogen embrittlement and stress corrosion cracking of metals, and particularly of corrosion resistant alloys. Hydrogen embrittlement (HE) and stress corrosion cracking (SCC) are important phenomena that impact many industrial operations. Laboratory test results are being used increasingly to assess the performance of steels and especially corrosion-resistant alloys toward hydrogen embrittlement and stress corrosion cracking. Because of the wide differences in responses of various corrosion-resistant alloys to corrosive environments, galvanic effects become especially important in assessing HE and SCC resistance. Also, most present methods of stressing samples involve the use of specimen restraining fixtures. To test a number of alloys and to avoid galvanic effects, a large number of fixtures are required. The costs and time to obtain these fixtures are high. Therefore, a need existed for a method of stressing samples without the associated problem of galvanic corrosion or the need to use fixtures to stress the samples.
Recent reports show that about one-third of present deep well completions in the U.S. use corrosion-resistant alloys for corrosion control. Many of these deep wells will be acidized using either hydrochloric acid or mixtures that include HCl. Therefore, the likelihood of HCl contacting various corrosion-resistant alloys is quite high. Most of the experimental work on effects of acidizing environments on corrosion-resistant alloys has emphasized general corrosion, especially at elevated temperatures. However, some evidence shows that stress corrosion cracking can result with the presence of H.sub.2 S in room temperature hydrochloric acid. Since the dissolution of sulfide-containing scales during acidizing may provide a source of sulfide ions, this form of cracking must be considered in using corrosion-resistant alloys. Corrosion inhibition can mitigate stress corrosion cracking in HCl; however only cursory examinations have been made of inhibition on cracking behavior of corrosion resistant alloys.
Because of the many requirements for stress corrosion cracking tests in HCl, a new test sample assembly was needed. Testing fixtures sufficiently resistant to corrosion in HCl+H.sub.2 S to provide freedom from solution contamination and sufficient strength were not readily available. In addition, the time and cost needed to manufacture testing fixtures from exotic alloys is excessive. Therefore, a system was needed to stress the samples without the requirement for stressing fixtures. While there are stressing methods available that do not require fixtures, these methods are either not quantitative with respect to applied stress (i.e., u-bends), or require welding.
One type of prior art test assembly is a "double cantilever" assembly comprising a metal bar having a slot formed in one end. A wedge is driven into the slot to provide stress, and the assembly with the wedge is then subjected to the test environment. These assemblies also include grooves extending along their length and holes formed to attach to devices for application of tensile forces. The amount of machining required for these assemblies is excessive in situations where large numbers of tests are to be run, such as when a particular alloy is to be tested over a wide range of temperatures or with a range of corrosive fluids.